Glass that is fairly clear in color and highly transmissive to visible light (e.g., at least 75% transmissive, or even more preferably at least 80% transmissive) is sometimes desirable. One way of achieving such as glass is to use very pure base glass materials (e.g., substantially free of colorants such as iron). However, base materials with a high degree of purity are expensive and thus not always desirable and/or convenient. In other words, for example, the removal of iron from glass raw materials has certain practical and/or economical limits.
As can be appreciated from the above, glass raw materials (e.g., silica, soda ash, dolomite, and/or limestone) typically include certain impurities such as iron. The total amount of iron present is expressed herein in terms of Fe2O3 in accordance with standard practice. However, typically, not all iron is in the from of Fe2O3. Instead, iron is usually present in both the ferrous state (Fe2+; expressed herein as FeO, even though all ferrous state iron in the glass may not be in the form of FeO) and the ferric state (Fe3+). Iron in the ferrous state (Fe2+; FeO) is a blue-green colorant, while iron in the ferric state (Fe3+) is a yellow-green colorant. The blue-green colorant of ferrous iron (Fe2+; FeO) is of particular concern when seeking to achieve a fairly clear or neutral colored glass, since as a strong colorant it introduces significant color into the glass. While iron in the ferric state (Fe3+) is also a colorant, it is of less concern when seeking to achieve a glass fairly clear in color since iron in the ferric state tends to be weaker as a colorant than its ferrous state counterpart.
In view of the above, it is apparent that there exists a need in the art for a new glass composition which enables a glass to have fairly clear color and/or high visible transmission, without having to resort to extremely pure (i.e., free of iron) glass raw materials.
An object of this invention is to provide a glass that has fairly clear color and/or high visible transmission.
Another object of this invention is to provide a glass having a visible transmission of at least 75% (more preferably at least 80%, and most preferably at least 85%), wherein in making the glass a batch therefor includes a base glass (e.g., soda lime silica glass) and in addition comprising (or consisting essentially of in certain embodiments), by weight percentage:
Optionally, other colorants such as neodymium oxide (e.g., Nd2O3) may also be provided in certain example embodiments. While cerium oxide is preferred in many embodiments, its presence is not a requirement. In other embodiments of this invention, the cerium oxide (e.g., CeO2) in the glass batch may be either replaced or supplemented by sodium nitrate (NaNO3) as an oxidizer.
Another object of this invention is to fulfill one or more of the above-listed objects and/or needs.
Certain example embodiments of the invention fulfill one or more of the above-listed objects and/or needs by providing a method of making glass, the method comprising:
providing a glass batch comprising:
melting the batch and forming a resulting glass that has visible transmission of at least 75%, a transmissive a* color value of xe2x88x921.0 to +1.0, and a transmissive b* color value of xe2x88x921.0 to +1.5.
Certain other example embodiments of this invention fulfill one or more of the above-listed objects and/or needs by providing a glass comprising:
Certain other example embodiments of this invention fulfill one or more of the above-listed objects and/or needs by providing a method of making glass, the method comprising providing a glass batch comprising:
Certain other example embodiment of this invention fulfill one or more of the above-listed objects and/or needs by providing a glass comprising:
Glasses according to different embodiments of this invention may be used, for example, in the automotive industry (e.g., windshields, backlites, side windows, etc.), in architectural applications, for patterned glass applications, solar cell applications, and/or in other suitable applications.
Certain glasses according to this invention utilize soda-lime-silica flat glass as their base composition/glass. In addition to base composition/glass, a unique colorant portion is provided in order to achieve a glass that is fairly clear in color and/or has a high visible transmission. An exemplary soda-lime-silica base glass according to certain embodiments of this invention, on a weight percentage basis, includes the following basic ingredients:
Other minor ingredients, including various conventional refining aids, such as SO3, carbon, and the like may also be included in the base glass. In certain embodiments, for example, glass herein may be made from batch raw materials silica sand, soda ash, dolomite, limestone, with the use of salt cake (SO3) and/or Epsom salts (e.g., about a 1:1 combination of both) as refining agents. Preferably, soda-lime-silica based glasses herein include by weight from about 10-15% Na2O and from about 6-12% CaO. While a soda-lime-silica base glass set forth above is preferred in certain embodiments of this invention, this invention is not so limited. Thus, other base glasses (e.g., borosilicate glass) may instead be employed in alternative embodiments of this invention.
In addition to the base glass (e.g., see Table 1 above), in making glass according to the instant invention the glass batch includes materials (including colorants and/or oxidizers) which cause the resulting glass to be fairly neutral in color and/or have a high visible light transmission. These materials may either be present in the raw materials (e.g., small amounts of iron), or may be added to the base glass materials in the batch (e.g., cerium, erbium, etc.). In certain preferred embodiments, the resulting glass has visible transmission of at least 75%, more preferably at least 80%, and most preferably at least 85%.
In certain embodiments of this invention, in addition to the base glass, the glass batch includes materials as set forth in Table 2 below (in terms of weight percentage of the total glass composition):
The batch is melted and glass formed using the known float process. Optionally, in certain example embodiments of the invention, neodymium oxide (e.g., Nd2O3) may be added to the batch, as exemplified below in Table 3 according to a second example embodiment of this invention (the material listed in Table 3 are in addition to the base glass described above).
In certain embodiments of this invention (e.g., first and/or second embodiments above), the colorant portion is substantially free of other colorants (other than potentially trace amounts). However, it should be appreciated that amounts of other materials (e.g., refining aids, melting aids, colorants and/or impurities) may be present in the glass in certain other embodiments of this invention without taking away from the purpose(s) and/or goal(s) of the instant invention. It is noted that while the presence of cerium oxide is preferred in many embodiments of this invention, it is not required in all embodiments. Moreover, it is possible to use little or no Er in certain embodiments of this invention.
In other embodiments of this invention, the cerium oxide (e.g., CeO2) may be either replaced or supplemented by NaNO3 in the glass batch; see the third, fourth and fifth embodiments below (the batch materials in Tables 4-6 below are in addition to the base glass raw materials described above).
In the fifth embodiment (see Table 6 above), cerium oxide (e.g., CeO2) and sodium nitrate (NaNO3) may be combined as oxidizers, so as to cause the effects of equations (1) and (2) below. Accordingly, one or both of cerium oxide and/or sodium nitrate may be provided in this fifth embodiment.
It is noted that in certain embodiments herein, the amount of total iron may even be less than 0.10%.
The above batches are melted and the float process used to form glass (e.g., soda lime silica glass) in a known manner.
The total amount of iron present in the glass batch and in the resulting glass, i.e., in the colorant portion thereof, is expressed herein in terms of Fe2O3 in accordance with standard practice. This, however, does not imply that all iron is actually in the form of Fe2O3 (see discussion above in this regard). Likewise, the amount of iron in the ferrous state (Fe+2) is reported herein as FeO, even though all ferrous state iron in the glass batch or glass may not be in the form of FeO. As mentioned above, iron in the ferrous state (Fe2+; FeO) is a blue-green colorant, while iron in the ferric state (Fe3+) is a yellow-green colorant; and the blue-green colorant of ferrous iron is of particular concern, since as a strong colorant it introduces significant color into the glass which can sometimes be undesirable when seeking to achieve a neutral or clear color.
According to certain example embodiments of this invention, the presence of cerium oxide (e.g., CeO2) as an oxidizer in the glass batch acts as a chemical decolorizer since during melting of the glass batch it causes iron in the ferrous state (Fe2+; FeO) to oxidize to the ferric state (Fe3+) as illustrated by the following equation:
Fe2++Ce4+=Fe3++Ce3+xe2x80x83xe2x80x83(1)
Equation (1) shows that the presence of cerium oxide in the glass batch causes an amount of the strong blue-green colorant of ferrous iron (Fe2+; FeO) to oxidize into the weaker yellow-green ferric iron colorant (Fe3+) during the glass melt (note: some ferrous state iron will usually remain in the resulting glass, as potentially may some Ce4+). Accordingly, a significant portion of the CeO2 added to the original glass batch prior to the melt is transformed during the melt into Ce2O3 which is present in the resulting glass. The aforesaid oxidation of the iron tends to reduce coloration of the glass, and does not significantly decrease visible light transmission of the resulting glass (in certain instances, this may even causes visible transmission to increase). However, those of skill in the art will appreciate that there still exists significant coloration in the glass due to the ferric iron if only the iron and cerium oxide are provided. In other words, it has been found that adding cerium oxide to only iron containing glass is not sufficient to achieve a desired fairly clear or neutral color.
It is noted that, like Fe2O3, the phrase xe2x80x9ccerium oxidexe2x80x9d as used herein refers to total cerium oxide (i.e., including cerium oxide in both the Ce4+ and Ce3+ states).
As mentioned above, the cerium oxide may be replaced by, or supplemented with, sodium nitrate in certain example embodiments of this invention. In embodiments where sodium nitrate (NaNO3) is provided in the glass (e.g., see Tables 3-5 above), it functions in a manner similar to cerium oxide as shown in the below equation (but note the potential for oxygen bubbles). In particular, like cerium oxide, sodium nitrate can be added to the glass batch as an oxidizer to cause an amount of the strong blue-green colorant of ferrous iron (Fe2+; FeO) to oxidize into the weaker yellow-green ferric iron colorant (Fe3+) during the glass melt (note: some ferrous state iron will usually remain in the resulting glass):
Fe2++NO3=Fe3++NO2+xc2xdO2xe2x80x83xe2x80x83(2)
Those skilled in the art will recognize that the most of the nitrate (e.g., sodium nitrate) added to the glass batch decomposes during the melt so that some burns off as NOx while other parts of it end up in the glass as Na2O. While sodium nitrate (NaNO3) is utilized as an oxidizer in Tables 4-6 above, the instant invention is not so limited. For example, other nitrates (e.g., potassium nitrate KNO3, or any other suitable nitrate) may be used instead of or in addition to sodium nitrate in alternative embodiments of this invention.
In order to compensate for the color caused by the ferric iron resulting from the addition of the cerium oxide and/or sodium nitrate, it has been found that adding erbium oxide (e.g., Er2O3 or any other suitable stoichiometric form) and/or neodymium oxide (e.g., Nd2O3 of any other suitable stoichiometric form) causes the color of the resulting glass to become more clear (i.e., more neutral as the a* and/or b* color value(s) move(s) toward neutral 0). Erbium oxide acts as a pink colorant, while neodymium oxide acts as a purple colorant. One or both of Er and/or Nd apparently acts to physically compensate for the iron color, thereby making the color of the glass more neutral which is desirable in certain embodiments of this invention, while enabling the glass to still have high visible transmission.
It will be appreciated by those skilled in the art that the addition of cerium oxide and/or sodium nitrate (see equations (1) and (2) above) results in a glass with a lower xe2x80x9credoxxe2x80x9d value (i.e., less iron in the ferrous state FeO). In this regard, the proportion of the total iron in the ferrous state (FeO) is used to determine the redox state of the glass, and redox is expressed as the ratio FeO/Fe2O3, which is the weight percentage (%) of iron in the ferrous state (FeO) divided by the weight percentage (%) of total iron (expressed as Fe2O3) in the resulting glass. Due to the presence of the cerium oxide and/or sodium nitrate, the redox of glass according to certain example embodiments of this invention is rather low; in particular, glass according to certain example embodiments of this invention may have a redox value (i.e., FeO/Fe2O3) of less than or equal to 0.25, more preferably less than or equal to 0.20; even more preferably less than or equal to 0.15, and most preferably less than or equal to 0.13. Moreover, resulting glass according to certain example embodiments of this invention may include iron in the ferrous state (FeO) in an amount (wt. %) of less than or equal to 0.020%, more preferably less than or equal to 0.015%, and most preferably less than or equal to 0.011%.
It is noted that glass according to this invention is often made via the known float process in which a tin bath is utilized. It will thus be appreciated by those skilled in the art that as a result of forming the glass on molten tin in certain exemplary embodiments, small amounts of tin or tin oxide may migrate into surface areas of the glass on the side that was in contact with the tin bath during manufacture (i.e., typically, float glass may have a tin oxide concentration of 0.05% or more (wt.) in the first few microns below the surface that was in contact with the tin bath).
In view of the above, glasses according to certain example embodiments of this invention achieve a neutral or substantially clear color and/or high visible transmission. In certain embodiments, resulting glasses according to certain example embodiments of this invention may be characterized by one or more of the following transmissive optical or color characteristics when measured at a thickness of from about 1 mm-6 mm (most preferably a thickness of about 0.219 inches; this is a non-limiting thickness used for purposes of reference only) (Lta is visible transmission %):
As can be seen from Table 7 above, glasses of certain embodiments of this invention achieve desired features of fairly clear color and/or high visible transmission, while not requiring iron to be eliminated from the glass composition. This may be achieved through the provision of the unique material combinations described herein.